Conventionally, efforts have been made to continue the weaving operation of a loom as long as possible by avoiding interruption of the weaving process. However, prolonged weaving operations have their disadvantages as will be explained below. In order to enable an uninterrupted weaving operation for hours on end, certain conditions must be met. A first condition is that the supply of weft yarns and warp yarns is substantially continuous. Another condition requires that the weft and warp yarns are resistant to breakage to be able to withstand the mechanical strain or wear and tear during the weaving operation of looms, particularly high speed mechanical looms.
It is known from "Melliand Textile Reports", 1990, Vol. 11, pages 859 to 860, to monitor the weaving process on looms in an all encompassing manner in order to assure that the proportion of faulty fabrics is held as small as possible. The just mentioned monitoring involves, among others, the arrangement of at least one thread monitor or weft stop motion device upstream of the weft feeders, that is between the weft feeders and the thread supply spools. Such a sensor or weft stop motion device provides an electrical signal in response to a broken weft thread, or when a weft thread is missing altogether, or when the weft has a fault. The electrical signal is used for stopping the loom prior to the respective weft feeder running empty, for example when the fault is a break in the weft thread upstream of the weft feeder.
European Patent Publication EP 0,195,469 B2 discloses a system that is based on the use of a weft stop motion device in a position described above, however with the improvement of avoiding stopping the loom by using a weft thread supply system with at least a first and a second weft supply spool, each cooperating with a weft feeder operated in a so-called weft mixing weaving operation. The known system works in such a way that upon detection of a weft thread break within one or more weft supply passages between the respective yarn supply spool and the respective weft feeder, the corresponding weft feeder is switched off and another weft feeder receives a signal for rotating faster to double its weft thread supply capacity thereby avoiding stopping the loom. In this manner it is possible to continue the weaving without interruption in spite of the disablement of one of the roving bodies by increasing the weft supply capacity of another roving body in the supply system.
Furthermore, it is known to measure the length of a pattern repetition in a weaving operation and to compare the actually measured pattern length with rated tolerance values stored in a memory. The comparing takes place at the completion of each pattern to see whether the just completed length of fabric is within the rated or given limits. If the just completed pattern length is outside the permissible limits, a signal is generated to stop the loom and to indicate the deviation in a display.
Other efforts in the past have also improved the mechanical capabilities of looms to enable high speed looms to operate continuously for hours on end without interrupting the weaving operation.
While a continuous weaving operation without interruption is efficient in certain respects, it has its disadvantages because when the time comes that the loom must be stopped, fabric faults cannot be avoided, particularly in looms equipped with a clutch brake combination between the loom drive motor and the main loom drive shaft. This drawback is due to the fact that the clutch brake combination is subject to a certain time delay between the stop signal and the actual stopping of the loom drive shaft and such delay becomes longer in duration the longer the loom was operating without interruption.
Observations in practice have shown that a weaving operation continuing for several hours on high speed looms without interruption of the weaving operation have the disadvantage that the environmental conditions caused by such continuous weaving adversely influence the braking characteristic of the loom brake, specifically the braking operation of the clutch brake combination. This adverse influence causes the above delay between the stop signal and the actual stopping of the loom drive shaft due to the high relative humidity in the weaving hall and the high fly lint which in combination form a sliding film on the brake components of the clutch brake combination. This sliding film causes in response to a brake activating signal a type of aqua planing which delays the loom stopping until this film is rubbed off. This delay in the braking action following the stop signal causes misaligned positions of the main loom drive shaft compared to positions that the main loom drive shaft should assume in accordance with programmed brake and stop positions. Thus, the delay in the braking action leads, for example to the fact that the sley and thus the reed mounted on the sley perform a beat-up along the beat-up line which in turn leads to densification of the fabric. As a result, when the loom is started again, so-called start markings become visible in the fabric which diminishes the fabric quality.